Women who have lymphedema or have had lymph nodes removed as a result of breast cancer treatment need to wear compression sleeves when flying. The outside pressure when flying fluctuates wildly and can cause inefficient lymph flow. Inefficient flow can lead to fluid build up and swelling.
Another reason wearing compression sleeves is imperative is the fact that flying is a sedentary activity. Limited muscle movement also diminishes lymph flow. Overexertion, such as lifting heavy bags, after sitting for so long can cause an inflammatory response, again leading to swelling. In addition to wearing compression sleeves, try to do subtle stretches and seat exercises to increase lymph flow and decrease the likelihood of blood clots forming.